1. Field of the Invention
The present invention relates to an apparatus and method for digital up converting in a mobile communication system. More particularly, the present invention relates to a digital up converting apparatus for supporting a variety of frequency bands with minimum hardware and an operation method thereof.
2. Description of the Related Art
In general, a digital up converter included in a digital transceiver board of a mobile communication system performs functions of interpolation, filtering, and frequency shifting using a digital signal processing technology. In more detail, the digital up converter frequency-shifts a baseband signal input from a channel card and up-converts the frequency-shifted baseband signal into an intermediate frequency signal. At this time, the digital up converter performs interpolation and increases a data rate of the signal, and performs digital filtering and removes a noise besides a signal band used for communication.
On the other hand, the standard of a Long Term Evolution (LTE) system provides five frequency bandwidths, i.e., frequency bandwidths of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, and 20 MHz. However, the conventional art does not provide a technique for supporting all of the five frequency bandwidths in a single hardware structure. Undoubtedly, the conventional art may process several kinds of bandwidth signals through a single hardware structure. However, in this case, there is a problem that, as a pass bandwidth decreases compared to a sampling frequency, a tap count of a Channel Shaping Filter (CSF) suddenly increases.
Table 1 below illustrates a filter tap count necessary to support the five bandwidth signals defined in the LTE standard in a digital up converter according to the conventional art.
TABLE 1BandwidthFilter tap count20 MHz 51 Taps10 MHz101 Taps 5 MHz201 Taps 3 MHz401 Taps1.4 MHz 601 Taps
As illustrated in Table 1, as a pass bandwidth decreases compared to a sampling frequency, the digital up converter according to the conventional art requires a great number of filter taps count. To support all of the five bandwidth signals, as illustrated in FIG. 1, the digital up converter should have 601 taps 100 required by 1.4 MHz that is the lowest bandwidth among the five bandwidths. That is, to process a 1.4 MHz bandwidth signal using a sampling frequency of 30.72 MHz, the digital up converter requires multipliers of the number corresponding to 601 as taps of a channel shaping filter. Accordingly, there is a problem that a hardware realization complexity increases. More particularly, the multiplier is one of Arithmetic Logic Units (ALUs) having high realization complexities in a digital hardware.
Accordingly, there is a problem that, from the hardware complexity side, it is inefficient to support a variety of frequency bandwidths by the conventional digital up converter.